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. 2022 May 22;15(10):3706.
doi: 10.3390/ma15103706.

Infill Density Influence on Mechanical and Thermal Properties of Short Carbon Fiber-Reinforced Polyamide Composites Manufactured by FFF Process

Lucia-Antoneta Chicos  1 , Mihai Alin Pop  2 , Sebastian-Marian Zaharia  1 , Camil Lancea  1 , George Razvan Buican  1 , Ionut Stelian Pascariu  1 , Valentin-Marian Stamate  1
Affiliations

Infill Density Influence on Mechanical and Thermal Properties of Short Carbon Fiber-Reinforced Polyamide Composites Manufactured by FFF Process

Lucia-Antoneta Chicos et al. Materials (Basel). .

Abstract

In three-dimensional (3D) printing, one of the main parameters influencing the properties of 3D-printed materials is the infill density (ID). This paper presents the influence of ID on the microstructure, mechanical, and thermal properties of carbon fiber-reinforced composites, commercially available, manufactured by the Fused Filament Fabrication (FFF) process. The samples were manufactured using FFF by varying the infill density (25%, 50%, 75%, and 100%) and were subjected to tensile tests, three-point bending, and thermal analyses by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). It was shown that the samples with 100% ID had the highest values of both tensile, 90.8 MPa, and flexural strengths, 114 MPa, while those with 25% ID had the lowest values of 56.4 MPa and 62.2 MPa, respectively. For samples with infill densities of 25% and 50%, the differences between the maximum tensile and flexural strengths were small; therefore, if the operating conditions of the components allow, a 25% infill density could be used instead of 50%. After DSC analysis, it was found that the variation in the ID percentage determined the change in the glass transition temperature from 49.6 °C, for the samples with 25% ID, to 32.9 °C, for those with 100% ID. TGA results showed that the samples with IDs of 75% and 100% recorded lower temperatures of onset degradation (approximately 344.75 °C) than those with infill densities of 25% and 50% (348.5 °C, and 349.6 °C, respectively).

Keywords: carbon fiber; fused filament fabrication; infill density; mechanical properties; polyamide; thermal properties.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Results after tensile tests; (a) load–displacement curves; (b) tensile strength, modulus, and relationship between tensile strength and infill density.
Figure 2
Figure 2
Results after three−points flexural tests: (a) flexural test load–displacement curves; (b) flexural strength, modulus, and relationship between flexural strength and infill density.
Figure 3
Figure 3
Micrographs of the PAHT CF15 filament. (a) Longitudinal section/view (200×); (b) cross-section (200×).
Figure 4
Figure 4
Micrographs of the samples with 25% infill density. (a,b) Longitudinal section (200×); (c) cross-section top side and (d) bottom side (50×).
Figure 5
Figure 5
Micrographs of the samples with 50% infill density. (a,b) Longitudinal section (200×); (c,d) top side of the cross-section at 50× and 200×.
Figure 6
Figure 6
Micrographs of the samples with 75% infill density. (a,b) Longitudinal section (200×); (c,d) bottom and top side of the cross-section (200×).
Figure 7
Figure 7
Micrographs of the samples with 100% infill density. (a,b) Longitudinal section from the interior of the sample (50×, 200×); (c,d) longitudinal section from the lateral side of the sample (50×, 200×); (e,f) bottom and top side of the cross-section (50×).
Figure 7
Figure 7
Micrographs of the samples with 100% infill density. (a,b) Longitudinal section from the interior of the sample (50×, 200×); (c,d) longitudinal section from the lateral side of the sample (50×, 200×); (e,f) bottom and top side of the cross-section (50×).
Figure 8
Figure 8
DSC thermogram for PAHT CF15 filament.
Figure 9
Figure 9
Results of DSC analysis for sample with 25% infill density.
Figure 10
Figure 10
DSC analysis for sample with 50% infill density.
Figure 11
Figure 11
DSC thermogram for sample with 75% infill density.
Figure 12
Figure 12
DSC curves related to sample with 100% infill density.
Figure 13
Figure 13
TGA curves for PAHT CF15 filament.
Figure 14
Figure 14
TGA results for sample with 25% infill density.
Figure 15
Figure 15
Thermogravimetric analysis curves for sample with 50% infill density.
Figure 16
Figure 16
TGA results for sample with 75% infill density.
Figure 17
Figure 17
Thermogravimetric analysis results for sample with 100% infill density.
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